Rotating disk data storage devices and particularly rigid disk magnetic disk drives have always been sensitive to even occasional contact between the transducer head, which normally flies above the disk surface, and the disk data surface. Such contact is the major cause of lost data and catastrophic drive failure. The problem becomes more severe as data densities are increased and drive size is reduced. Increased data density is attained using higher relative velocities between head and disk; smaller, more delicate head structures and thinner magnetic coatings with each of these parameters making more severe the problem of head-disk contact.
The greatest potential for damage to the drive, if not anticipated and compensated for, is the prolonged contact between head and disk when power to the spindle motor is interrupted, either when the device is powered down or power is otherwise interrupted and the disks coast to a stop. This problem has been overcome by moving the heads to a landing zone, usually at the disk inner diameter and braking the disk spindle assembly to terminate disk rotation.
Two techniques have been most commonly used to resolve the problem of head-disk contact following power interruption. One method is to retract the heads to the landing or unloading zone using the kinetic energy of the rotating spindle. The DC spindle motor windings function to generate a current as the spindle motor spins down, to drive the actuator to a retracted position following which the spindle can be dynamically braked by shorting the spindle motor windings. Another technique used to retract the actuator to a landing position is the provision of capacitive storage which is charged during normal power on operation and is switched to drive the actuator when power to the device is turned off or otherwise interrupted.
These techniques are adequate and successful in larger drives including 51/4 and 31/2 inch form factors, but problems develop in the design of very small drives such as those conforming to the Personal Computer Memory Card Industry Association (PCMCIA) Type II and smaller dimensional standards. PCMCIA Type III drives have an overall height of 10.5 millimeters, while the PCMCIA Type II drives have an overall height of only 5 millimeters. With a length and width of approximately 31/4 and 2 inches respectively, there is very little space for the disk assembly, spindle motor, actuator and transducer assembly, the surrounding sealed enclosure and the various data channel, servo, motor driver and control circuits. The disk and spindle assembly have sufficient kinetic energy to generate the power required to drive the actuator when power is interrupted; however, it has not been possible to convert the kinetic energy to electrical energy in motors of the sizes used in the confined space of the PCMCIA type II and smaller form factors.
As the size of disk drives continues to shift toward smaller and smaller form-factors it is apparent that new technologies will have to be developed to overcome the many new complications associated with this paradigm shift. A major complication discovered recently while developing a prototype for a PCMCIA Type II form factor disk drive was the lack of any usable spindle system energy, energy that has been traditionally used to provide for the retract/unload operation in larger form-factor drives, thus necessitating the use of an alternative energy storage mechanism, such as a capacitor. Another initial complication was the physical size of the capacitor required to provide for the retract/unload operation in the traditional capacitor assisted retract circuit. The size determined to be sufficient to provide for the retract/unload operation could not be made to fit in the highly limited physical space for components.